Technique Description
In Auger spectroscopy, the excitation source is a finely focused electron
beam. Upon sample bombardment, a transfer of energy occurs which excites
a core electron into an orbital of higher energy. Once in this excited state,
the atom has two possible modes of relaxation: emission of a X-ray, or emission
of an Auger electron. In both processes, the emitted particle will have
an energy characteristic of the parent element. An energy spectrum of the
detected electrons shows peaks assignable to the elements present. The ratios
of the intensities of Auger electron peaks can provide a quantitative determination
of surface composition. The Auger multiprobe is capable of producing elemental composition spectra, surface images, selective elemental line scans and maps, and depth profiles. Imaging is achieved through detection of secondary, backscattered and Auger electrons. Elemental line scans detect concentrations along a line, while a map, which is considerably more time consuming, detects elemental distribution over an area. Auger analysis involves the top most 20 Å only, making it an extremely surface sensitive technique.
Depth profiles are obtained by employing a controlled sputtering process which enables elemental concentration to be plotted as a function of depth. 'Sputtering' is a process in which an ion gun is used to remove a few angstroms of the top most surface of a sample. Sputtering and analysis are alternated until the desired depth is reached. Thicknesses in layered samples are calibrated by comparison to the sputtering rate of a known thickness of SiO2. Auger depth profiling is well suited for conductive samples composed of thin multilayers where thickness or interface properties must be determined.
Elemental composition with a sampling depth of 20 ÅDetects elements higher than Li in the periodic table.
Good sensitivity for light elementsDepth profile, with depth resolution better than 20ÅElemental spatial distribution (map, line)Secondary electron imaging with spatial resolution 0.1µm
ESCA can analyze insulators and give chemical state information
but can not image surfaces. Both have sputtering capabilities but AES is
better equipped to produce depth profiles.SEM can produce images with much better resolution.EDX analysis provides compositional information with a
sampling depth of 1-2 µm, Auger sampling depth is three orders of magnitude
smaller at about 20 Å. Conducting solids (metals, alloys, semiconductors, thin films) with dimensions less than 2 cm diameter and 1 cm high may be analyzed. Samples must be clean and free from any high vapor pressure material. It is important that the specimen surface not be handled.
Generally samples are analyzed "as received" and then again after removal of 20 Å of material by light sputtering. This is done to insure that the surface is free of organic or other incidental contaminants.The surface elemental composition can usually be obtained in an hour or less. When maps or depth profiles are requested, analysis time can range between 1-3 hours per sample
Samples must be conductiveQuantitative detection sensitivity is reliable to ~1.0
atomic percent depending on the elementBeam damage possible with some materialsAccuracy of qualitative analysis is limited to ± 30%
if published sensitivity factors are used, better quantification is possible
(± 10%) if standards closely resembling the sample are usedElements H and He are undetectableBack to SCIC home page.